For those who have stuck to New Year resolutions and actually managed to eat five portions of fruit and veg a day in January, some unpleasant news arrives from America. It's not enough. According to new guidelines just released in the US, nine portions is now the minimum intake we should be aiming for.

America is not alone in the belief that the five-a-day rule is no longer sufficient. Australians are encouraged to eat seven portions of fruit and veg. In France and Canada, the figure is 10. There might be some discrepancy in what constitutes a portion and whether duplication is allowed, but the message is clear. According to guidelines, you have to eat more fruit and veg to be healthy in America and France than you do in Britain. Maybe fish and chips are better for us than we thought.

And it's not just food. The US guidelines also stress the importance of trying to fit in - between the endless salads - 90 minutes of exercise on most days of the week. Again, the advice from the Department of Health in this country is more modest. Thirty minutes, five days a week should do the trick, it says.

Which all begs a number of questions. Who's got it right? Are we kidding ourselves with our piddling five portions? And, more importantly, how on earth do you fit nine portions of fruit and veg and 90 minutes of exercise into an average Monday? The latter is already exercising minds on the other side of the Atlantic.

The view of Dr Madelyn Fernstrom, director of the Weight Management Centre at the University of Pittsburgh Medical Centre, is typical: "When the bar is always being set higher," she says, "it can sabotage people who want to change their lifestyle. People get discouraged thinking that whatever they do isn't enough."

Indeed, many nutritionists think the UK has got it about right. The car- loving, burger-munching Americans are deluding themselves. The French are fantasists. This is not about how many portions citizens of various countries actually eat: very few in any country meet the target (though most do better than us). The British guidelines might lack ambition, but at least they are anchored in reality.

"We still have some way to go before we're eating five portions a day," says Dr Hannah Theobald of the British Nutrition Foundation. "We should be encouraging people to eat more, but putting up the recommendations may put people off eating even three portions. Such a move is likely to be counter-productive."

It would be for Isobel Martin, a single mother from Manchester, who has managed to incorporate five portions into her diet - just. "I do it, but it usually means forcing down a couple of tangerines in the evening when I don't want them," she says. "After reaching five, being told I was still four out would be heartbreaking." And 90 minutes of exercise a day? "Forget it."

Nevertheless, Dr David McCarthy, reader in human nutrition at London Metropolitan University, says the new US guidelines are based on sound science. "The Dash (Dietary Approaches to Stop Hypertension) trial in the US on fruit and vegetable consumption and blood pressure is the main source of the data supporting this recommendation. It showed unequivocally that blood pressure was reduced when subjects doubled their intake of fruit and vegetables. The benefits of a diet richer in fruit and veg on lowering the risk of certain cancers - such as colon cancer - also underpins the new US guidelines."

If nine portions are better for us, shouldn't that be our target? In an ideal world yes, but let's learn to walk first. Few think that the US strategy of nutritional shock and awe should be adopted in the UK. "I was taken aback after hearing the US guidelines," says Dr McCarthy. "I feel they're just setting us up for failure."

On the other hand, what we mustn't do is regard the five-a-day rule as the nutritional finishing post. "Five portions are a minimum intake, but this aspect of the message is not taken on board," says Dr McCarthy. Dr Theobald agrees that, while the US has started producing optimum intake guidelines, our own are just a basic requirement: "It's often forgotten, but the UK guidelines say at least five a day."